Pneumatic fractionating apparatus

ABSTRACT

Apparatus for fractionating particulate material has an upright shaft whose bottom end is bounded by an oblique, perforated end wall. An opening in the shaft spacedly above the lower edge of the end wall communicates with a feed hopper through an opening whose flow section may be adjusted by means of a valve plate so as to keep a portion of the end wall free of the material to be fractionated. The top portion of the shaft is connected to a settling and collecting vessel from which air is drawn by a suction system so that atmospheric air is drawn through the end wall. The latter may be withdrawn from time to time to release accumulating particles of a type not transferred to the collecting vessel by the air stream.

United States Patent Terhorst 1 Jan. 28, 1975 [54] PNEUMATICFRACTIONATING l,894.020 1/1933 Chance 209/495 X 2, l Suggs .1 39 R [75]Inventor: Harold Terhorst Emmerich Primary E.\'am1'nerFrank W. LutterGermany Assistant E.\'aminerRalph J. Hill [73] Assignee: Probat-Werkevon Gimborn 8L C0. I y 8 Hr F am B 'mim K.G., Emmerich, Germany 22Filed: Mar. 10, 1973 [57] f f ABSTRACT I h Apparatus or ractionatingparticu ate matcria as an [21] Appl' 342361 upright shaft whose bottomend is bounded by an oblique, perforated end wall. An opening in theshaft [30] F i A li ti P i i D t spacedly above the lower edge of theend wall com- Apr 27 972 Germany l I N 2220785 municates with a feedhopper through an opening whose flow section may be adjusted by means ofa 52 11.5. C1. 209/139 R 209/467 Valve Plate as keep Of end Wall free511 1111. C1. 13 0711 4/08 of the material to be fracmnated- The topPmio" of f Search I I I H R the shaft lS connected to a settling andCollecting VCS- 2 sel from which air is drawn by a suction system sothat atmospheric air is drawn through the end wall. The [56] ReferencesCited latter may be withdrawn from time to time to release accumulatingparticles of a type not transferred to the UNITED STATES PATENTS O 3collecting vessel by the air stream 1,323,306 12/1919 Morse 2 9| 81,850,719 3/1932 Herz 209/141 x 14 Claims, 3 Drawing FiguresFLTENTEDJAHZB i975 SHEET 1 [IF 2 PATENTEB JAN 2 8 I975 Y SHEET 2 OF 2PNEUMATIC FRACTIONATING APPARATUS This invention relates to thefractionation of a solid, particulate mixture, and particularly topneumatic apparatus for separating particle fractions from a mixturethereof.

It is known to fractionate solid, particulate mixtures having uniformparticle sizes up to about 30 mm by means of a gas stream entering themixture through a perforated plate on which the mixture is supported,whereby a fraction of lower specific gravity is entrained in the airstream and recovered therefrom in purified form, whereas impurities ofhigher specific gravity accumulate on the plate and may be withdrawnseparately. The known pneumatic fractionating or classifying devicesthat have been found effective are relatively costly to build andoperate, and less elaborate devices achieve only insufficient separationof the fractions.

It is a primary object of this invention to provide a fractionatingapparatus for particulate mixtures which is simple and inexpensive tobuild and operate, yet cleanly separates fractions of different specificgravity in a mixture of approximately uniform particle size or particlesotherwise differing in their interaction with a rising stream of gas.

In its more specific aspects, the invention provides apparatus in whicha conduit is mounted on a support in an upright position. An obliquelysloping end wall formed with a multiplicity of apertures downwardlybounds the axially terminal bottom portion of the bore in the conduitwhen the apparatus is in its operative condition. The particulatematerial to be fractionated is fed to the bottom portion of the conduit,and a stream of fluid is passed through the apertures in the end wallinto the bore of the conduit, and thence into a collecting vesselcommunicating with the axially terminal top portion of the conduit by asuction blower which produces and maintains a pressure differentialbetween the several parts of the apparatus and a source of the fluid,such as ambient. atmospheric air. The fluid stream, when suitablymatched to the feeding rate for the mixture, entrains only lighterparticles and deposits them in the collecting vessel, whereas a heavierfraction accumulates on the apertured end wall, and may be withdrawntherefrom from time to time.

Other features, additional objects, and many of the attendant advantagesof this invention will readily be appreciated as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the appended drawing in which:

FIG. 1 shows fractionating apparatus of the invention in elevation andpartly in section; and

FIGS. 2 and 3 show modifications of the apparatus of HO. 1 infragmentary corresponding views.

Referring now to the drawing in detail, and initially to H6. 1, there isseen a feed hopper 1 containing the particulate mixture 2 which it isdesired to fractionate. An upright valve plate or flap 3 held in adesired vertical position by a clamping screw 4 controls the size of anopening 22 which admits material from the obliquely sloping bottom wallof the hopper 1 to an end wall 5 of a shaft 6. The wall 5 is a screen orperforated plate whose apertures are preferably small enough not to passthe particles of the mixture 2. The end wall 5 slopes obliquely relativeto the vertical axis of the shaft 6 toward the circumferential wallportion which is common to the shaft 6 and the hopper l and divides thehopper from the shaft, the latter being a straight sheetmetal conduithaving a bore of square cross section.

The axially terminal, upper portion of the bore in the shaft 6communicates with a collecting vessel 7 whose upper part is cylindricaland whose bottom wall conically tapers toward a central slide valve 21.A suction system including an exhaust blower, not shown, communicateswith the top portion of the vessel 7 through a suction conduit 8.

The shaft 6 and hopper l are supported on a sheet metal base 20laterally closed in three directions so as to provide guidance to an airstream represented by arrows 9 toward the face of the end wall 5 outsidethe bottom portion of the shaft 6, and to guide the air stream throughthe apertures in the end wall 5 toward the circumferential portion ofthe shaft 6 which is formed with the opening 22.

A lower oblique edge 10 on each of two opposite shaft walls guides pins,obscured in the drawing, which project from the lower edge of the endwall 5 at right angles to the plane of the drawing. The top edge of theapertured end wall 5 projects beyond the shaft 6 and carries a handle14. it is releasably secured to the shaft 6 by a permanent magnet 16.Prongs 15 project from the bottom edge of the end wall 5 throughrespective openings, not explicitly shown, in the axial wall part 24 ofthe shaft 6 spacedly below the opening 22 so as to secure the end wallin the illustrated operative position, in which a pocket 11 is formedbetween the end wall 5 and the upright wall part 24 of the shaft 6 belowthe opening 22.

A pan 19 positioned in the base 20 catches any fines that may dropthrough the apertures in the end wall 5. When the end wall 5 is pulledobliquely upright and toward the left, as viewed in the drawing, bymeans of the handle 14, all material carried on the wall 5 drops intothe pan 19 through the gap opening between the lower edge of the endwall 5 and the axial wall part 24.

A short duct 17 arranged on the shaft 6 at about one third of its heighton the axial wall opposite the opening 22 is provided with a hinged flap18 which permits the duct 17 to be sealed or to be opened to any desiredflow section for admitting ambient air when the exhaust blower (notshown) draws air from the vessel 7.

The afore-described apparatus operates as follows:

When the non-illustrated blower produces a pressure differential betweenthe two faces of the end wall 5, a stream of air is guided into thebottom portion of the shaft 6 by the base 20 in such a direction as toblow particles on the wall 5 upward and toward the opening 22. Theparticulate mixture 2 flows from the hopper 1 into the shaft 6 under theforce of gravity at a rate determined partly by the size of the opening22 between the valve plate 3 and the top rim of the wall part 24 set bythe clamping screw 4. The rate of particle flow is also affected by therate at which particles are removed from the end wall 5 toward thecollecting vessel 7 and by the resistance of the air stream 9. The valveplate 3 is readily set in such a manner that the portion of the end wall5 in the shaft 6 near the handle 14 is free from particles of themixture at all times, and the air is freely discharged in this area fromthe apertures in the wall 5, while an almost stagnant body of particlesaccumulates in the pocket 11.

Under such operating conditions, the lighter particles, presumed to bethose of the product to be purified, are lifted into the vessel 7 wherethey settle from the air stream whose velocity suddenly decreases as itemerges from the relatively narrow shaft 6 into the wide vessel 7. Theproduct particles may be withdrawn through the valve 21 from time totime, or the valve may be replaced by a screw conveyor for continuousproduct discharge without loss of suction, if so desired. Secondary airadmitted through the duct 17 permits a high air velocity to bemaintained in the top portion of the shaft 6 for sufficient liftingaction without causing excessive turbulence in the fractionation orclassification area immediately above the end wall 5, and particularlyin the pocket 11 in which a heavy fraction is trapped, and from which itmay be released from time to time after closing the opening 22, andshutting down the non-illustrated blower as soon as all productparticles have been blown from the end wall into the collecting vessel7.

The suction system represented in the drawing only by the suctionconduit 8 may include a cyclone for removing entrained fine particlesfrom the withdrawn air, and further includes the necessary drive for theblower, electric switch gear, and like conventional elements, not shown.

If it is desired for any reason to interrupt operation of the apparatusand to empty the shaft 6, the handle 14 may be released from the magnet16 after the valve plate 3 was lowered until it engages the rim of thewall part 24, and the end wall 5 may be pivoted on its prongs and thenon-illustrated guide pins to drop the particles from the shaft 6 intothe pan 19. The contents of the hopper 1 may thereafter be discharged byraising the valve plate 3.

Practically perfect separation of two particle fractions differing inspecific gravity, but approximately equal in size, is achieved by theoblique inclination of the apertured end wall 5 toward the pocket 11.Due to gravity and agitation by the passing air, the heavier particlestend to migrate downward along the end wall 5 while the lighterparticles tend to migrate upward. The

air velocity is highest through the upper portion of the wall 5 wherethere is no overlying particulate material, and it is very low in thepocket 11 where the particle layer is thickest. The lighter particles,therefore, migrate toward the area of greatest air velocity and tend tobe entrained by the rapid stream of fluid while they are almost freefrom the heavier fraction. The heavier particles accumulating in thepocket 11 are held there by gravity and are not exposed to an air streamrapid enough to dislodge them. Very little air normally enters the shaft6 through the opening 22, the particulate material 2 in the hopper 1providing a practically airtight seal, and such air as may be drawnthrough the opening 22 passes above the pocket 11.

The purity of the separated fractions of a given mixture depends, underotherwise constant conditions, on the angle of inclination of the endwall 5. The illustrated fractionation apparatus is intended forcontinuous operation on a uniform product so that the angle ofinclination of the end wall 5 is fixed at an optimum value determinedpreviously by trial and error.

The apparatus of FIG. 1 is readily modified for fully automaticoperation as is shown in FIG. 2. The operating cycle is controlled by arotary timing switch 50 connected by conductors 58, 60 to solenoidvalves of reversible pneumatic motors 52, 56. The pressure linessupplying compressed air to the cylinders of the motors 52, 56 andassociated manual shut-off valves have been omitted from the drawing.

The piston rod of the motor 52 is attached to a valve plate 54, closelysimilar in structure and function to the afore-described valve plate 3,and shifts the valve plate 54 upward from the illustrated position inwhich it radially closes the shaft 6 when the valve of the motor 52 isenergized.

The shaft 6 is downwardly bounded under normal operating conditions by aflat screen 54 guided obliquely relative to the vertical axis of theshaft 6 by two guide rails 62 of which only one is seen in FIG. 2. Asillustrated in FIG. 2, the solenoid valve of the motor 56 is energized,and the piston rod of the motor 56 holds the screen 54 in a position inwhich it permits accumulated impurities 58 to be discharged by gravityfrom the bottom of the shaft 6.

When the current in the conductors 60 is shut off by the switch 50, themotor 56 pushes the screen into its normal operating position in whichit permits the entry of air into the shaft 6 from below, butsubstantially prevents discharge of particulate solids. When,thereafter, the conductors 58 receive current from the switch 50, thevalve plate 54 is raised and the apparatus of FIG. 2 assumes a conditionanalogous to that shown in FIG. 1 until the switch 50 restores thepositions of the valve plate 54 and of the screen 54 after a periodwhose length may be set on the switch 50 in a conventional manner.

FIG. 3 shows a modification 0f the device of FIG. 2 in which impuritiesmay be released from the shaft 6 by pivoting the screen 30 normallyserving as an obliquely inclined bottom wall for the shaft. The upperedge of the screen 30, otherwise similar to the screen 54, is attachedto the shaft 6 by means of a pivot shaft 32. An arm 42 fixedly attachedto the screen 30 is hingedly fastened to the piston rod of adouble-acting pneumatic motor 40 controlled by a built-in solenoid valveas described above with reference to the motor 56.

When the solenoid is energized, the motor 40 pivots the screen 30 intothe illustrated position. When the solenoid is deenergized, compressedair in the motor 40 swings the screen 30 counterclockwise, as viewed inFIG. 3, against a sealing plate 34 mounted on the shaft 6 by means ofreleasable fasteners for vertical adjustment as indicated by a doublearrow.

The sealing rail determines the angle at which the screen 30 is inclinedrelative to the vertical axis of the shaft 6, and thus permits theapparatus to be adjusted for the properties of material to be processed.

Other variations and modifications of the illustrated examples of theinvention will readily suggest themselves to those skilled in the art,and it will be appreciated that this invention, within the scope andspirit of the appended claims, may be practiced otherwise than asspecifically disclosed.

I claim:

1. Apparatus for fractionating particulate material comprising, incombination:

a. a support;

b. a conduit mounted on said support in a position which is upright inthe operative condition of the apparatus,

1. said conduit having an axis and an axial wall circumferentiallybounding an axial bore in said conduit,

2. said bore having axially terminal top and bottom portions bounded byrespective upper and lower terminal parts of said axial wall,

3. said axial wall being formed with an opening spacedly adjacent saidlower terminal part thereof;

c. an end wall formed with a multiplicity of apertures and inclinedrelative to said axis.

1. said end wall downwardly bounding said bottom portion in saidoperative condition;

2. the lowermost portion of said end wall and said lower terminal partbounding a pocket extending downward from said opening;

d. feeding means for feeding the particulate material to be fractionatedto said opening;

e. a collecting vessel communicating with said top portion; and

f. pressure means for passing a stream of fluid through said aperturesinto said bore, and through said bore into said collecting vessel.

2. Apparatus as set forth in claim 1, wherein said feeding meansincluding a hopper communicating with said bore through said opening.

3. Apparatus as set forth in claim 2, wherein said hopper extends upwardfrom said opening for gravity flow of said material into said bore, saidfeeding means further including valve means for controlling the rate ofsaid flow.

4. Apparatus as set forth in claim 3, wherein said valve means include aclosure member secured to said conduit for movement between a pluralityof positions in which said closure member defines respective differentflow sections of said opening.

5. Apparatus as set forth in claim 4, further comprising means forsecuring said closure member in each of said positions.

6. Apparatus as set forth in claim 1, further comprising means forsecuring said end wall in each of a plurality of positions of differentangular inclination relative to said axis.

7. Apparatus as set forth in claim 1, further comprising dischargingmeans for discharging from said bottom portion a fraction of saidmaterial accumulating in said pocket.

8. Apparatus as set forth in claim 7, wherein said discharging meansinclude means for withdrawing said lowermost portion of said end wallfrom said lower terminal part. and for thereby opening a downwardlydirected gap between said lowermost portion and said lower terminalpart.

9. Apparatus as set forth in claim 8, further comprising guide means forsubstantially maintaining the oblique inclination of said end wallrelative to said axis during said withdrawing.

10. Apparatus as set forth in claim 7, further comprising operatingmeans for operating said feeding means and said discharging means intimed sequence.

11. Apparatus as set forth in claim 10, wherein said operating meansinclude means for alternatively operating said feeding means and saiddischarging means.

12. Apparatus as set forth in claim 7, wherein said discharging meansinclude means for pivoting said end wall away from the position in whichsaid end wall bounds said bottom portion.

13. Apparatus as set forth in claim 1, further comprising guide meansfor guiding said stream of fluid toward a face of said end wall outsidesaid pocketin a direction toward said opening.

14. Apparatus as set forth in claim 1, wherein said pressure meansinclude means for withdrawing said fluid from said collecting vessel ata pressure lower than atmospheric pressure, said apertures communicatingwith the ambient atmosphere.

1. Apparatus for fractionating particulate material comprising, incombination: a. a support; b. a conduit mounted on said support in aposition which is upright in the operative condition of theapparatus,
 1. said conduit having an axis and an axial wallcircumferentially bounding an axial bore in said conduit,
 2. said borehaving axially terminal top and bottom portions bounded by respectiveupper and lower terminal parts of said axial wall,
 3. said axial wallbeing formed with an opening spacedly adjacent said lower terminal partthereof; c. an end wall formed with a multiplicity of apertures andinclined relative to said axis,
 1. said end wall downwardly boundingsaid bottom portion in said operative condition;
 2. the lowermostportion of said end wall and said lower terminal part bounding a pocketextending downward from said opening; d. feeding means for feeding theparticulate material to be fractionated to said opening; e. a collectingvessel communicating with said top portion; and f. pressure means forpassing a stream of fluid through said apertures into said bore, andthrough said bore into said collecting vessel.
 2. said bore havingaxially terminal top and bottom portions bounded by respective upper andlower terminal parts of said axial wall,
 2. the lowermost portion ofsaid end wall and said lower terminal part bounding a pocket extendingdownward from said opening; d. feeding means for feeding the particulatematerial to be fractionated to said opening; e. a collecting vesselcommunicating with said top portion; and f. pressure means for passing astream of fluid through said apertures into said bore, and through saidbore into said collecting vessel.
 2. Apparatus as set forth in claim 1,wherein said feeding means including a hopper communicating with saidbore through said opening.
 3. APparatus as set forth in claim 2, whereinsaid hopper extends upward from said opening for gravity flow of saidmaterial into said bore, said feeding means further including valvemeans for controlling the rate of said flow.
 3. said axial wall beingformed with an opening spacedly adjacent said lower terminal partthereof; c. an end wall formed with a multiplicity of apertures andinclined relative to said axis,
 4. Apparatus as set forth in claim 3,wherein said valve means include a closure member secured to saidconduit for movement between a plurality of positions in which saidclosure member defines respective different flow sections of saidopening.
 5. Apparatus as set forth in claim 4, further comprising meansfor securing said closure member in each of said positions.
 6. Apparatusas set forth in claim 1, further comprising means for securing said endwall in each of a plurality of positions of different angularinclination relative to said axis.
 7. Apparatus as set forth in claim 1,further comprising discharging means for discharging from said bottomportion a fraction of said material accumulating in said pocket. 8.Apparatus as set forth in claim 7, wherein said discharging meansinclude means for withdrawing said lowermost portion of said end wallfrom said lower terminal part, and for thereby opening a downwardlydirected gap between said lowermost portion and said lower terminalpart.
 9. Apparatus as set forth in claim 8, further comprising guidemeans for substantially maintaining the oblique inclination of said endwall relative to said axis during said withdrawing.
 10. Apparatus as setforth in claim 7, further comprising operating means for operating saidfeeding means and said discharging means in timed sequence. 11.Apparatus as set forth in claim 10, wherein said operating means includemeans for alternatively operating said feeding means and saiddischarging means.
 12. Apparatus as set forth in claim 7, wherein saiddischarging means include means for pivoting said end wall away from theposition in which said end wall bounds said bottom portion. 13.Apparatus as set forth in claim 1, further comprising guide means forguiding said stream of fluid toward a face of said end wall outside saidpocket in a direction toward said opening.
 14. Apparatus as set forth inclaim 1, wherein said pressure means include means for withdrawing saidfluid from said collecting vessel at a pressure lower than atmosphericpressure, said apertures communicating with the ambient atmosphere.